William J. Coughlin, who traversed four continents as a foreign correspondent before guiding a 10,000-circulation North Carolina newspaper to a Pulitzer Prize for its investigation into cancer-causing chemicals in the municipal water supply, died May 8 at a hospice in Bolivia, N.C. He was 91.

The cause was liver cancer, said his former wife Patricia Conlon.

Mr. Coughlin served in London and Moscow for the McGraw-Hill World News, edited the weekly magazine Missiles and Rockets and was a correspondent in Asia and the Middle East for the Los Angeles Times, which included coverage of the Vietnam War. After he left the Times in 1975, he briefly was a public affairs director and foreign policy adviser for Sen. John V. Tunney (D-Calif.).

After other editing jobs, he landed at the Washington Daily News — a family-owned newspaper in a lumber and fertilizer-manufacturing region of eastern North Carolina. He rose to executive editor.

The work that led to the Pulitzer began when Mr. Coughlin noticed the fine print on the back of his water bill that said tests had been performed on the local water supply and the results could be picked up at city hall.

He assigned the task to cub reporter Betty Gray, who only had been at the paper for less than two months after working 12 years at her father’s insurance office. At that point, she barely knew how to use her word processor, much less sift through reams of documents about chemicals that “didn’t really look that suspicious to me,” as she told the New York Times after the Pulitzer win.

With the help of reporter Mike Voss, she interviewed state environmental and health officials and took water samples that revealed carcinogens in the drinking water at many times the level beyond federal regulations.

The reporters dug up evidence that at least three mayors, plus local, state and federal officials, had known about the problem and ignored it for the greater part of a decade.

Under Mr. Coughlin, the Daily News began printing dozens of articles on the scandal starting in September 1989. After one of the first pieces ran, Gray recalled getting hold of a memo that a state epidemiologist sent to a city official.

“The memo said, ‘Your tap water is unsafe to drink and you should start drinking bottled water,’” Gray told the New York Times in 1990. “But after I told the city I had it, they continued to deny that there was a problem.”

The U.S. Marine Corps and National Guard soon arrived with truckloads of potable water and, that October, Mayor J. Stancil Lilley lost reelection by a landslide. State officials began working on a plan for rigorous water monitoring, and the Environmental Protection Agency used the incident to set new water quality guidelines nationwide.

“One thing is for absolutely certain in my mind, is that without Bill Coughlin as our executive editor, there certainly would not have been a Pulitzer Prize for the Daily News,” Gray told the Daily News after Mr. Coughlin’s death. “His directorship was crucial in that endeavor . . . He had the experience, the expertise . . . he knew how to do it.”

After the Pulitzer win, Mr. Coughlin said the investigation was unusual for the paper, which at the time focused on the sleepy doings of city council and Rotary Club meetings.

“I will say we haven’t had this much excitement in this town since the Union cavalry and the Confederate cavalry chased each other up Main Street in 1862, and there’s been nothing like that since,” Mr. Coughlin told the Associated Press.

William James Coughlin was born May 29, 1922, in Washington, D.C., and moved with his family to Los Angeles at 16. He served in the Army Air Forces during World War II and flew P-38 fighters in the Pacific.

He was a 1947 graduate of Stanford University, which he had entered before his military service, and also received a master’s degree in journalism from Stanford in 1950. His thesis was published in book form two years later, “Conquered Press: the MacArthur Era in Japanese Journalism.”

Mr. Coughlin left the Daily News in 1990 to teach journalism at Francis Marion University in Florence, S.C., according to Conlon. He split his time between his homes in Southport, N.C., and western Ireland.

His marriages to Geraldine Tobias and Patricia Kelleher (now Conlon) ended in divorce. Survivors include three children from his first marriage, Kevin Coughlin of Wilmington, N.C.; Kerry Coughlin of Seattle; and Kelly Webb of Park City, Utah; three grandchildren; and a great-granddaughter.

“I feel it’s a little ironic after having worked in Moscow and Vietnam and Beirut — to find my Pulitzer in a little town in North Carolina,” Mr. Coughlin said in 1990. “It says if you set your standards high enough, you can be just as good as big-town newspapers.”